In power and free conveyor systems, carriers are movable along a free track by a powered chain or the like and are transferred to various locations in the system by track switches. It is common to provide an encoder unit on the carrier which includes a particular code arrangement of contacts, magnetic snesors, optical sensors, or other sensing devices. When the carrier with the encoder is moved past a fixed readout unit along the track and the position or code setting of the sensing devices on the encoder corresponds to the position or code of the sensing devices on the readout unit, signals are produced which are then transmitted to a readout circuit which will actuate the track switch for routing the carrier to the proper portion of the system.
Such systems are well known and are shown and described in U.S. Pat. Nos. 3,126,837, 3,140,669 and 3,171,362.
One of the problems in connection with such systems is that there sometime occur spurious signals or false signals. An additional problem is that the circuitry heretofore used has limited the versatility of the system in terms of optional operation such as for recirculating the carriers where portions of the system are filled or shutting down the system. The present invention is intended to obviate or minimize these problems.
The invention includes a logic circuit that is electrically isolated from spurious and false signals; wherein the logic circuitry is separate from the readout portion of the circuitry; wherein digital logic is utilized to improve the versatility of the system; and wherein there is time filtering of the input signals to the logic circuit to minimize false signals.